1. Field of the Invention
The present invention relates to a touch screen driving device.
2. Discussion of the Related Art
An user interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been used in portable information appliances and has been expanded to the use of home appliances. A mutual capacitive touch screen has been recently considered as an example of a touch screen for implementing the touch UI. The mutual capacitive touch screen can sense a proximity input as well as a touch input and also can recognize respective multi-touch (or multi-proximity) inputs.
The mutual capacitive touch screen includes Tx channels, Rx channels crossing the Tx channels, and sensor capacitors formed at crossings of the Tx channels and the Rx channels. Each sensor capacitor has a mutual capacitance. A touch screen driving device senses changes in voltages charged to the sensor capacitors before and after a touch operation and decides whether there is a touch (or proximity) input using a conductive material. Further, the touch screen driving device determines a position of the touch input when there is a touch input. To sense the voltages charged to the sensor capacitors, a Tx driving circuit applies a driving signal to the Tx channels, and an Rx driving circuit samples a small change in the voltages of the sensor capacitors in synchronization with the driving signal and performs an analog-to-digital conversion.
In general, examples of a factor reducing a signal-to-noise ratio (SNR) of touch data include a channel noise depending on the arrangement of channels and structural characteristics of the touch screen, and an external noise. Examples of the external noise include a floating body, 3-wavelength noise, and a charge noise. Examples of the channel noise include a high frequency noise/low frequency noise of an input signal, channel DC offset, and an interference noise between channels.
A deviation between touch data of channels is generated by different resistor parameters and different capacitor parameters in the touch screens of various structures. Even in the same touch screen, a deviation between touch data input to a touch integrated circuit (IC) is generated by the variation of an influence of an external environment (for example, PCB routing, external noise, etc.) depending on a position and the variation of the resistor parameter and the capacitor parameter. The deviation reduces the signal-to-noise ratio of the touch data and thus reduces touch reliability.